Title

Author

Defense Date

2008

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Physiology

First Advisor

Bruce Spiess

Abstract

Decompression sickness (DCS) results from a sudden decrease in ambient pressure leading to super-saturation of tissues with inert gas and subsequent bubble formation within both tissues and blood. Perfluorocarbons (PFC) are able to dissolve vast amounts of non-polar gases. The administration of intravenous (I.V.) PFC emulsions reduce both morbidity and mortality of DCS, but the mechanism of this protective effect has not yet been demonstrated. Juvenile Dorper cross sheep between 16 and 24 kg (n=31) were anaesthetized and instrumented for physiological monitoring, the administration of I.V. fluids and sampling of arterial and mixed venous blood. Animals were placed in a hyperbaric chamber and compressed to 6.0 atmospheres absolute for 30 minutes, then rapidly decompressed. Upon chamber exit animals were randomly assigned to receive 6cc/kg of either PFC or saline control over 5 minutes beginning immediately after chamber exit. They were also randomized to receive one of 4 breathing gases post-chamber: 100% O2, 80/20 N2/O2, 50/50 HeO2, or 80/20 HeO2. Blood samples were drawn at 5, 10, 15, 30, 60, and 90 minutes to examine whole-body oxygenation. Respiratory gases were monitored and recorded in real-time using mass spectroscopy to examine nitrogen washout. PFC administration increased arterial oxygen content (16.30±0.27 vs. 14.75±0.25 mL/dL, p<0.0001), oxygen delivery (14.83±0.28 vs. 13.44±0.25 mL/minute/kg, p=0.0004), and tissue oxygen consumption (3.37±0.14 vs. 2.76±0.13 mL/minute/kg, p=0.0018) over saline control, but did not increase mixed venous oxygen content (12.45±0.26 vs. 11.74±0.24 mL/dL, p=0.0558) or extraction ratio (0.23±0.012 vs. 0.21±0.011, p=0.1869). PFC administration lowered the plateau of the curve, increasing the amount of nitrogen washout vs. saline control (22.22±1.566 vs. 15.98±1.380 mmHg, p= 0.0074). Breathing 80/20 HeO2 increased the decay constant of the curve, increasing the rate of washout vs. breathing 100% O2 (0.03176±0.001044 vs. 0.03096±0.0009402, p=0.5777). PFC improves whole-body oxygenation after severe DCS and increases the amount of nitrogen washout. Although the effects of both PFC and 80/20 HeO2 breathing were statistically significant the magnitude of the nitrogen washout effect is quite small, and unlikely to be clinically significant. Thus it is likely that the improved oxygenation is responsible for the previously-observed therapeutic effects of PFC in treating DCS.